4,399 research outputs found
Studies of (GaAI)As injection lasers operating with an optical fiber resonator
The characteristics of an optical fiber external resonator in conjunction with (GaAl)As stripe geometry lasers are described. We have observed a 6â10% reduction in the threshold current and have obtained 150 ps pulses at gigahertz repetition rates. The fiber resonator has also been used to quench selfâpulsations in a (GaAl)As injection laser. In order to explain many of our results we have used a model that uses the conventional semiconductor rate equations modified by the addition of saturable electron traps and the effects of the external cavity. Our results predict many of the selfâlocking effects observed in injection lasers operating in an external cavity. Furthermore, the degree of selfâlocking will be a strong function of the external cavity length and the density of saturable absorbers
Free-induction-decay magnetometer with enhanced optical pumping
Spin preparation prior to a free-induction-decay (FID) measurement can be
adversely affected by transverse bias fields, particularly in the geophysical
field range. A strategy that enhances the spin polarization accumulated before
readout is demonstrated, by synchronizing optical pumping with a magnetic field
pulse that supersedes any transverse fields by over two order of magnitude. The
pulsed magnetic field is generated along the optical pumping axis using a
compact electromagnetic coil pair encompassing a micro-electromechanical
systems (MEMS) vapor cell. The coils also resistively heat the cesium (Cs)
vapor to the optimal atomic density without spurious magnetic field
contributions as they are rapidly demagnetized to approximately zero field
during spin readout. The demagnetization process is analyzed electronically,
and directly with a FID measurement, to confirm that the residual magnetic
field is minimal during detection. The sensitivity performance of this
technique is compared to existing optical pumping modalities across a wide
magnetic field range. A noise floor sensitivity of
was achieved in a field of approximately , in close
agreement with the Cram\'{e}r-Rao lower bound (CRLB) predicted noise density of
.Comment: 10 pages, 7 figure
An X-Ray Regenerative Amplifier Free-Electron Laser Using Diamond Pinhole MIrrors
Free-electron lasers (FELs) have been built ranging in wavelength from
long-wavelength oscillators using partial wave guiding through ultraviolet
through hard x-ray FELs that are either seeded or start from noise (SASE).
Operation in the x-ray spectrum has relied on single-pass SASE due either to
the lack of seed lasers or difficulties in the design of x-ray mirrors.
However, recent developments in the production of diamond crystal Bragg
reflectors point the way to the design of regenerative amplifiers (RAFELs)
which are, essentially, low-Q x-ray free-electron laser oscillators (XFELOs)
that out-couple a large fraction of the optical power on each pass. A RAFEL
using a six-mirror resonator providing out-coupling of 90% or more through a
pinhole in the first downstream mirror is proposed and analyzed using the
MINERVA simulation code for the undulator interaction and the Optics
Propagation Code (OPC) for the resonator. MINERVA/OPC has been used in the past
to simulate infrared FEL oscillators. For the present purpose, OPC has been
modified to treat Bragg reflection from diamond crystal mirrors. The six-mirror
resonator design has been analyzed within the context of the LCLS-II beamline
under construction at the Stanford Linear Accelerator Center and using the HXR
undulator which is also to be installed on the LCLS-II beamline. Simulations
have been run to optimize and characterize the properties of the RAFEL, and
indicate that substantial powers are possible at the fundamental (3.05 keV) and
third harmonic (9.15 keV).Comment: 9 pages, 14 figure
Solar cell radiation handbook
The handbook to predict the degradation of solar cell electrical performance in any given space radiation environment is presented. Solar cell theory, cell manufacturing and how they are modeled mathematically are described. The interaction of energetic charged particles radiation with solar cells is discussed and the concept of 1 MeV equivalent electron fluence is introduced. The space radiation environment is described and methods of calculating equivalent fluences for the space environment are developed. A computer program was written to perform the equivalent fluence calculations and a FORTRAN listing of the program is included. Data detailing the degradation of solar cell electrical parameters as a function of 1 MeV electron fluence are presented
Chip-scale atomic magnetometer based on free-induction-decay
This thesis describes the implementation of an optically pumped caesium magnetometer containing a 1:5mm thick microfabricated vapour cell with nitrogen buffer gas, operating in a free-induction-decay configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarise the atomic sample;however, synchronous modulation of the light field actively drives the precession and maximises the induced spin coherence. Both amplitude- and frequency-modulation have been adopted producing noise floors of 3.4 pT / âHz and 15.6 pT/âHz, respectively,within a Nyquist limited bandwidth of 500 Hz in a bias field comparable to the Earth's (~50 ÎŒT). We investigate the magnetometers capability in reproducing time-varying magnetic signals under these conditions, including the reconstruction of a 100 pT perturbation using signal averaging.Additionally, we discuss a novel detection mode based on free-induction-decay that observes the spin precession dynamics in-the-dark using Ramsey-like pulses. This aids in suppressing the systematic effects originating from the light-atom interaction during readout, thus vastly improving the accuracy of the magnetometer whilst maintaining a sensitivity that is competitive with previous implementations. This detection technique was implemented further to measure the spin relaxation properties intrinsic to the sensor head, useful in determining the optimal buffer pressure that extends the spin lifetime and improves the sensor's sensitivity performance.This thesis describes the implementation of an optically pumped caesium magnetometer containing a 1:5mm thick microfabricated vapour cell with nitrogen buffer gas, operating in a free-induction-decay configuration. This allows us to monitor the free Larmor precession of the spin coherent Cs atoms by separating the pump and probe phases in the time domain. A single light pulse can sufficiently polarise the atomic sample;however, synchronous modulation of the light field actively drives the precession and maximises the induced spin coherence. Both amplitude- and frequency-modulation have been adopted producing noise floors of 3.4 pT / âHz and 15.6 pT/âHz, respectively,within a Nyquist limited bandwidth of 500 Hz in a bias field comparable to the Earth's (~50 ÎŒT). We investigate the magnetometers capability in reproducing time-varying magnetic signals under these conditions, including the reconstruction of a 100 pT perturbation using signal averaging.Additionally, we discuss a novel detection mode based on free-induction-decay that observes the spin precession dynamics in-the-dark using Ramsey-like pulses. This aids in suppressing the systematic effects originating from the light-atom interaction during readout, thus vastly improving the accuracy of the magnetometer whilst maintaining a sensitivity that is competitive with previous implementations. This detection technique was implemented further to measure the spin relaxation properties intrinsic to the sensor head, useful in determining the optimal buffer pressure that extends the spin lifetime and improves the sensor's sensitivity performance
LANDSAT D local user terminal study
The effect of the changes incorporated in the LANDSAT D system on the ability of a local user terminal to receive, record and process data in real time was studied. Alternate solutions to the problems raised by these changes were evaluated. A loading analysis was performed in order to determine the quantities of data that a local user terminal (LUT) would be interested in receiving and processing. The number of bits in an MSS and a TM scene were calculated along with the number of scenes per day that an LUT might require for processing. These then combined to a total number of processed bits/day for an LUT as a function of sensor and coverage circle radius
Muon and Cosmogenic Neutron Detection in Borexino
Borexino, a liquid scintillator detector at LNGS, is designed for the
detection of neutrinos and antineutrinos from the Sun, supernovae, nuclear
reactors, and the Earth. The feeble nature of these signals requires a strong
suppression of backgrounds below a few MeV. Very low intrinsic radiogenic
contamination of all detector components needs to be accompanied by the
efficient identification of muons and of muon-induced backgrounds. Muons
produce unstable nuclei by spallation processes along their trajectory through
the detector whose decays can mimic the expected signals; for isotopes with
half-lives longer than a few seconds, the dead time induced by a muon-related
veto becomes unacceptably long, unless its application can be restricted to a
sub-volume along the muon track. Consequently, not only the identification of
muons with very high efficiency but also a precise reconstruction of their
tracks is of primary importance for the physics program of the experiment. The
Borexino inner detector is surrounded by an outer water-Cherenkov detector that
plays a fundamental role in accomplishing this task. The detector design
principles and their implementation are described. The strategies adopted to
identify muons are reviewed and their efficiency is evaluated. The overall muon
veto efficiency is found to be 99.992% or better. Ad-hoc track reconstruction
algorithms developed are presented. Their performance is tested against muon
events of known direction such as those from the CNGS neutrino beam, test
tracks available from a dedicated External Muon Tracker and cosmic muons whose
angular distribution reflects the local overburden profile. The achieved
angular resolution is 3-5 deg and the lateral resolution is 35-50 cm, depending
on the impact parameter of the crossing muon. The methods implemented to
efficiently tag cosmogenic neutrons are also presented.Comment: 42 pages. 32 figures on 37 files. Uses JINST.cls. 1 auxiliary file
(defines.tex) with TEX macros. submitted to Journal of Instrumentatio
Muon and Cosmogenic Neutron Detection in Borexino
Borexino, a liquid scintillator detector at LNGS, is designed for the
detection of neutrinos and antineutrinos from the Sun, supernovae, nuclear
reactors, and the Earth. The feeble nature of these signals requires a strong
suppression of backgrounds below a few MeV. Very low intrinsic radiogenic
contamination of all detector components needs to be accompanied by the
efficient identification of muons and of muon-induced backgrounds. Muons
produce unstable nuclei by spallation processes along their trajectory through
the detector whose decays can mimic the expected signals; for isotopes with
half-lives longer than a few seconds, the dead time induced by a muon-related
veto becomes unacceptably long, unless its application can be restricted to a
sub-volume along the muon track. Consequently, not only the identification of
muons with very high efficiency but also a precise reconstruction of their
tracks is of primary importance for the physics program of the experiment. The
Borexino inner detector is surrounded by an outer water-Cherenkov detector that
plays a fundamental role in accomplishing this task. The detector design
principles and their implementation are described. The strategies adopted to
identify muons are reviewed and their efficiency is evaluated. The overall muon
veto efficiency is found to be 99.992% or better. Ad-hoc track reconstruction
algorithms developed are presented. Their performance is tested against muon
events of known direction such as those from the CNGS neutrino beam, test
tracks available from a dedicated External Muon Tracker and cosmic muons whose
angular distribution reflects the local overburden profile. The achieved
angular resolution is 3-5 deg and the lateral resolution is 35-50 cm, depending
on the impact parameter of the crossing muon. The methods implemented to
efficiently tag cosmogenic neutrons are also presented.Comment: 42 pages. 32 figures on 37 files. Uses JINST.cls. 1 auxiliary file
(defines.tex) with TEX macros. submitted to Journal of Instrumentatio
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